Plasma etching chambers are commonly used to etch one or more layers formed on a semiconductor substrate. During etching, the substrate is supported on a substrate support within the chamber. A substrate support typically includes a clamping mechanism. Edge rings can be disposed around the substrate support (i.e., around the substrate) for confining plasma to the space above the substrate and/or to protect the substrate support from erosion by the plasma. The edge rings, sometimes called focus rings, can be sacrificial (i.e., consumable) parts. Conductive and non-conductive edge rings are described in commonly-owned U.S. Pat. Nos. 5,805,408; 5,998,932; 6,013,984; 6,039,836 and 6,383,931.
Lithographic techniques can be used to form geometric patterns in a surface of the substrate. During a lithographic process, a pattern such as an integrated circuit pattern can be projected from a mask or reticle and transferred to a photosensitive (e.g., photoresist) coating formed on the surface of the substrate. Plasma etching, in turn, can be used to transfer the pattern formed in the photoresist layer to one or more layers formed on the substrate that underlie the photoresist layer.
During plasma etching, plasma is formed above the surface of the substrate by supplying radio-frequency (RF) electromagnetic radiation to a low pressure gas (or gas mixture). By adjusting the electrical potential of the substrate, charged species in the plasma can be directed to impinge upon the surface of the substrate and thereby remove material (e.g., atoms) therefrom.
Plasma etching can be made more effective by using gases that are chemically reactive with the material to be etched. So called “reactive ion etching” combines the energetic impinging effects of the plasma with the chemical etching effects of a reactive gas.
An etching byproduct may undesirably deposit on a lateral edge (e.g., bevel edge) or underside of the substrate. The byproduct deposition, which may be volatilized during subsequent processing, may have an adverse effect on process yield. In order to maximize yield, reduction in polymer buildup at the underside and on the bevel edge of the substrate would be desirable.